import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param pHead ListNode类 
     * @param k int整型 
     * @return ListNode类
     */
    public ListNode FindKthToTail (ListNode pHead, int k) {
        // write code here
        /*
        int len = 0;
        ListNode dummy = pHead;
        while (dummy != null) {
            len++;
            dummy = dummy.next;
        }
        if (k > len) {
            return null;
        }
        len -= k;
        while (len-- > 0) {
            pHead = pHead.next;
        }
        return pHead;
        */

        // 双指针
        ListNode fast = pHead, slow = pHead;
        while (k-- > 0) {
            if (fast == null) {
                return null;
            }
            fast = fast.next;
        }
        while (fast != null) {
            fast = fast.next;
            slow = slow.next;
        }
        return slow;
    }
}